We have demonstrated that human T-cell hybrids can be constructed by fusion of functional human T cells with the human T-cell line CEM-T15. CEM-T15 is a thioguanine-resistant mutant derived in our laboratory from the human T-cell line CEM. Furthermore, we have shown that hybrid clones generated in several different fusions have functions known to be present in normal T lymphocytes. In our initial screening we selected for T-cell hybrids with helper function as measured in the induction of B-cell differentiation. A number of these hybrids have been cloned and recloned several times, and helper function has been maintained. In addition, we have recently screened hybrids derived from other fusions for the capacity to synthesize and secrete interleukin-2, and several interleukin-2 producing hybrid clones were generated. Based on these promising preliminary results, the goals in this proposal are to: (1) further refine the techniques for human T-cell hybridization and in particular to establish a library of mutant human T-cell lines useful for hybridization to functional T-cells; (2) construct newer hybrid clones with antigen specificity. The biological characterization of these hybrids and their products will be performed using several in vitro biological assay systems routinely used in our laboratory. The goal of obtaining antigen specific human T-cell hybrids will be achieved by fusing enzyme-deficient lines derived in our laboratory (CEM-T15, T15-32, HAET6.6 and others) with antigen-specific interleukin-2 dependent cloned T-cell lines and with antigen-stimulated peripheral blood T lymphocytes. To facilitate the analysis of these hybrids and their factors we will produce monoclonal antibodies directed against both the hybrids and their secreted immunoregulatory molecules. We feel that T-cell hybrids and their products will be invaluable tools for detailed studies of regulation of antigen-specific human immune responses.